1. Technical Field
This invention relates generally to computer aided design/computer aided manufacture (CAD/CAM) equipment and more particularly to a Finite Element Analysis system having "intelligent", interactive user interface features which allow engineers without specialized knowledge in mathematical modeling to easily and interactively solve diverse problems.
2. Background Information
Throughout the technological explosion of the last 20 years, industry has found it increasingly necessary to model or predict the results of complex physical processes. Sophistication of product technology and the economics of the mass production process have imposed the requirement for techniques to accurately simulate the physical behavior of manufactured goods both during fabrication and in operation. The ramifications of the ability to fully model industrial processes bear upon each phase in the evolution of a product, resulting in: reduced design costs and time, the ability to design systems that would be prohibitively complex to design without modeling, reduced production costs and increased efficiency, and optimized product performance and life span.
For many years, the equations quantifying the fundamental laws which govern the behavior of matter have been known to scientists. The classical laws of mechanics, heat transfer, fluid mechanics, chemistry and electrodynamics fully describe the interactions which result in the behavior of most physical systems. However, the complexity of the mathematics prohibits solving these equations, by hand, for any but grossly oversimplified situations. For example, the solution of the mathematics describing the real-life situation exactly as posed in the practical world was impossible for such processes as: the drawing of molten tubing into fiber guide, the curing of plastic within the complicated geometry of a mold, the turbulent fluid flow in the internal workings of a pump, and the pressure and stress distributions about the wings and fuselage of aircraft. Hence, classical engineers were forced to resort to crude approximations and simplifications to make the mathematics more tractible. This resulted in the familiar iterative process of design by trial and error, with engineering analysis limited to providing "ballpark" estimates. Prototype development costs were thus phenomenal, and many highly sophisticated products which required "getting it right the first time" were economically unrealizable. Gross product overdesign and poor product performance are predictable results of this mode of operation.
This situation changed drastically with the development and propagation of modern computer technology. Predicated upon the availability of high speed digital computers, a numerical analysis technique called Finite Element Analysis (FEA) was developed. FEA utilizes a method of solution of the basic laws of physics which is unworkable without the capacity for performing many thousands of arithmetic operations each second. The finite element program is capable of in effect "living" the physical situation exactly as it would occur in nature.
FEA is thus able to totally describe the temporal behavior of virtually any system, no matter how complex. For example, a Finite Element Analysis would be capable of providing the stress field and temperature distribution at each point along the surface and interior of the space shuttle during reentry. Not all applications of FEA are equally esoteric. FEA is becoming increasingly popular with automobile manufacturers for optimizing both the aerodynamic performance and structural integrity of vehicles. Similarly, aircraft manufacturers rely upon FEA to predict airplane performance long before the first prototype is built. Rational design of semiconductor electronic devices is possible with Finite Element Analysis of the electrodynamics, diffusion, and thermodynamics involved in this situation. FEA is utilized to characterize ocean currents and distribution of contaminants. FEA is being applied increasingly to analysis of the production and performance of such consumer goods as ovens, blenders, lighting facilities and many plastic products. In fact, FEA has been employed in as many diverse fields as can be brought to mind, including plastics mold design, modeling of nuclear reactors, analysis of the spot welding process, microwave antenna design and biomedical applications such as the design of prosthetic limbs. In short, FEA is utilized to expedite design, maximize productivity and efficiency, and optimize product performance in virtually every stratum of light and heavy industry. This often occurs long before the first prototype is ever developed.
Finite Element Analysis derives its name from the manner in which the geometry of the object under consideration is specified. Basically, the FEA program must be provided with a "picture" of the geometric situation and a description of the properties of the material at each point within the picture. In this picture, the geometry of the system under analysis is represented by quadrilaterals and triangles of various sizes, which are called elements. The vertices of the elements are referred to as nodes. The mesh is composed of a finite number of elements (500-5,000 elements being typical). The mesh thus represents the physical space occupied by the object under analysis along with its immediate surroundings. The FEA program is informed of the composition of each element by assigning each element a material name. The program then refers to a table wherein the fundamental properties (such as thermoconductivity or electrical resistivity) of each material type is tabulated. Additionally, the conditions at the boundary of the object (i.e. radiation, convection, etc.) must be specified. In this fashion a model of the object and its environment is created. The model can then be processed by a computer using available Finite Element Analysis programs to simulate the effects on the object of a specified physical process.
The results of a Finite Element Analysis are most easily interpreted graphically. A particularly efficacious method is to superimpose isopotential lines (such as isopressure lines in a weather map or equilatitude lines in a topographical map) upon the basic geometry of the situation. For example, in viewing the thermal distribution within a system, lines connecting areas of equal temperature can be superimposed upon the model. The analyst can view successive time frames in this manner for an explicit pictorial representation of the evolution of the situation. For example, the temperature distribution at each point throughout an initially cold light bulb from the instant it is turned on until the temperature stops changing can be meaningfully illustrated in just such a manner.
For further detailed information on the FEA method, reference may be had to the text "State-Of-The-Art Surveys On Finite Element Technology" published by the American Society of Mechanical Engineers, 1983, the numerous publications cited therein, or other available literature on this subject.
Presently a Finite Element Analysis is an extremely formidable task to perform, usually not achievable by an engineer or scientist with ordinary skill in his area of expertise. Only a relatively small, select group of highly trained professionals, typically with PhD's in engineering or applied mathematics and additional years of direct experience with FEA are able to effectively utilize the technique. Such individuals must understand the intricacies of both the mathematics upon which FEA is based and the practical implementation of FEA. Even for those with the highly specialized training necessary to perform FEA, the technique is often cumbersome and labor intensive. A single analysis may require weeks to months of professional effort to complete. As a result, FEA has generally been confined to very large organizations which can afford to hire individuals specializing in FEA. Even in such large organizations, FEA is restricted mostly to the research and development centers and usually utilized only for the most pressing applications. The current situation is directly analogous to that which existed in the earliest days of the computer, when the application of a computer to a specific task required a uniquely trained individual to laboriously generate the program in machine language itself.
Currently there exists a dichotomy between systems which perform the actual finite analysis calculations and those which allow the user to enter the information necessary for analysis and to view the results. The latter is known as "CAD/CAM" systems while the former are referred to as "number-crunchers". Typically a user will create a model on a CAD system, transmit the information to a number-cruncher, run the analysis on the number-cruncher, transmit the results back to the CAD system and utilize the CAD system to view the results. The process must be repeated each time the user wishes to modify the model. Many problems are inherent to such fragmentation of the modeling process. Additionally, both the CAD systems and the number-crunchers impose individual barriers to effective modeling.
A major obstacle to performing Finite Element Analysis on existing systems lies in the user interface employed to provide the finite element program with information about the situation to be modeled and to interpret the results which the FEA program returns. In order to generate the proper program input to the FEA program with existing CAD systems, a user must be cognizant of the many nuances intrinsic to the technique. For example, the order in which the nodal points are specified can impact dramatically upon the amount of computer time necessary to perform the analysis. The user must develop an intuitive feeling for the physics of the situation in order to tailor the size of the elements to the gradients expected within them. Further, the analyst must develop an intimate familiarity with the details of the structure of the input file to the FEA program. Often, much or all of the input file is generated by manually entering numbers into the computer. The potential for specifying erroneous information is high and existing programs do not detect such errors as overlapping or undefined elements. Automatic model generation systems are available but these are designed primarily for applications other than FEA and generate models which are difficult to modify. After the analysis is performed, the results must be interpreted, which can involve combing through dozens of pages of computer printouts consisting of tables and numbers. In short, in addition to requiring specialized knowledge, existing interfaces make the data inputting and results interpretting operations of FEA extremely tedious and time consuming.
Currently there is no user interface system known to applicants specifically designed to support Finite Element Analysis model creation and results display. There are several commercially available CAD systems which offer some FEA support, but these all have severe limitations which curtail their usefulness. First, the available systems are powerful, generalized graphics systems which are designed mainly for integrated circuit, printed circuit board and drafting applications. FEA support packages are available secondary to the primary function of these systems. Second, these systems are usually extremely expensive even for a minimal system. Third, the finite element support packages which are available in these systems are extremely complicated to learn how to use. Expert personnel require extensive training to become facile with the use of these systems. Fourth, most of these packages do not allow specification of the complete input file for the analysis, so after using the support system the analyst must still massage the input file by hand. Fifth, few of these FEA support packages adequately provide for display of the results of the analysis. Sixth, extensive expert labor is often required to convert the files generated by these support systems to the format required by the user's FEA program and to convert the output of the FEA to a format acceptable to the support system. Users are thus forced to write their own programs to compensate for the deficiencies in the commercially available systems and as a result FEA is shrouded by mystique and often viewed as a "black art".
Commercial programs which perform the mathematics of the FEA process are available for use on a rental or a license basis. There are also several programs which are in the public domain. Thus it is not necessary for the end user to write his own Finite Element Analysis program. However, most of these programs are constrained to run on main frame or large mini computers which are priced far beyond the means of many potential users. Such number-crunchers are often operated in a time sharing mode which can result in long delays in analysis turnaround. Most large systems are not physically near the user who must communicate at low data transmission rates.
A few microcomputer based FEA systems have been developed. However, these generally comprise miniaturized versions of the main frame systems, exhibit limited processing and interactive capabilities, and require extensive training before they can be successfully operated.
A need thus exists for a Finite Element Analysis system which overcomes the limitations discussed above and is, in every sense, "within reach" of the ordinary engineer.